1. Field of the Invention
The present invention relates to an Fe--Cr--Al alloy foil which is produced by a rapidly solidifying process and which has resistance to high-temperature oxidation. Typical such materials are honeycomb materials used in exhaust gas converters of vehicles, and high-temperature heaters, or resistor materials.
2. Description of the Related Art
Various proposals have been hitherto made concerning Fe--Cr--Al alloys. For instance, Japanese Patent Laid-Open No. 58-177437 (U.S. Pat. No., 4,414,023) proposes an alloy containing Cr: 8 to 25 % by weight (hereinafter abbreviated to "wt %"), Al: 3 to 8 wt %, and all the rare-earth elements: up to 0.06 wt % with 0.002 to 0.05 wt % of Ce, La and Nd, the alloy further containing Si, Cu, Ni and the like added to improve anti-scale-peeling properties. The alloy is produced by performing cold rolling after hot rolling. In general, such an Fe--Cr--Al--REM alloy is used in, for instance, an exhaust gas converter of a vehicle, a resistor heater, or a radiation heater supporting member. However, when a foil obtained by a common rolling method, such as above, is used to form, for instance, a catalyst substrate in automotive exhaust gas systems of a vehicle with a width of not less than 50 mm, many problems arise if the converter is close to the engine where the temperature surrounding the converter is higher than normal. The converter is subjected to severe high-temperature, repeated oxidation and violent vibration each time the vehicle starts, accelerates or stops, resulting in oxide scales peeling off, thereby rendering the converter short-lived. With a common rolling method, it is technically difficult to produce a high Cr--Al foil having resistance sufficiently high to endure such environment. Further, heat treatment and cold rolling have to be repeatedly conducted, inevitably requiring high production costs.
In view of the above problems, the present inventors have previously cast their attention on a rapidly solidifying foil-production method in which rolling is omitted, and proposed to increase the amount of rare earth elements added so that anti-oxidation properties will be improved. To produce a foil by a rapidly solidifying method enables a high Cr--Al material, whose working is difficult, to be easily formed into sheets, and also assures a reduction in cost as well as a remarkable improvement in anti-oxidation properties. For instance, in Japanese Patent Laid-Open No. 63-42347, the present inventors have proposed to add rare earth materials or rare earth elements (REM) in a large amount of 0.06 to 0.30 wt % and to directly produce a foil by a rapidly solidifying method so that resistance to peeling of oxide film will be improved. In Japanese Patent Laid-Open No. 63-42356, the present inventors have proposed a rapidly solidifying method in which the content of Al is set within the range from 8 to 15 wt % so that anti-oxidation properties will be improved.
The addition of a large amount of REM or the method in which a high Al alloy is rapidly solidified does not involve any problem when such is performed on a laboratory scale, for instance, performed to produce narrow foils with a size of heating lot of 10 to 100 g, a foil width of 10 mm and a thickness of 50 .mu.m. However, said addition or said method entails various problems when applied to industrial-scale production of foils for use as materials in an exhaust gas converter of a vehicle, the foils having a width of not less than 50 mm and a size of heating lot of not less than 10 kg; that is, problems such as the clogging of nozzles, a decrease in the REM amount, and the occurrence of internal defects, arise. For these reasons, the proposals have not yet been reduced to practice.